Processes are known for preparing a penicillanic acid compound of the formula (2) from a halogenated penicillanic acid compound of the formula (1), by catalytic reduction with use of a noble metal catalyst, by reaction with organic tin hydride compound, by reaction with zinc, by electrolytic reduction method, by reaction with aluminum and a catalytic amount of metal lead or lead compound (for example, patent literatures 1 to 4, non-patent literatures 1 to 2).
(X and Y are a hydrogen atom or halogen atom, provided that X and Y are not hydrogen atoms at the same time, n is an integer of 0 to 2, R is carboxyl protecting group)
(n and R are same as above).    [patent literature 1] JP 1980-120588 A    [patent literature 2] JP 1982-169486 A    [patent literature 3] JP 1986-63683 A    [patent literature 4] JP 1989-66189 A    [non-patent literature 1] Nature, 201, 1124 (1964)    [non-patent literature 2] J. Chem. Soc., (C), 2123 (1968)
The catalytic reduction with use of a noble metal catalyst requires a large amount of an expensive noble metal catalyst and demands application of dangerous hydrogen pressure, therefore the method is not practical. The organic tin hydride compound is a reagent which is difficult to be used industrially and the organic tin compound is harmful. The process using zinc affords the desired product which is low in yield and purity. The electrolytic reduction requires special apparatus and has problems for industrial operation. Further, it is considered that the use of lead is preferably restricted from the viewpoint of environmental care.
An object of the invention is to provide a process for preparing a penicillanic acid compound of the formula (2) which is free of industrial problems, safe, simple in procedures and industrially advantageous.